Matrix How do I use the matrix mode on the casio fx -115 es

Let me explain how to create matrices. (If you know how to do it, skip to the operations on matricies, at the end.)

First you must set Matrix calculation
[MODE][6:Matrix]. Then By entering one of the numbers [1:MatA] or [2:Matb] or [3:MatC] you get to choose the dimensions of the matrix
(mxn]. Once finished entering the matrix you clear the screen.
The operations on matrices are available by pressing [Shift][Matrix]
[1:Dim] to change the dimension of a matrix (in fact redefining the matrix)
[2:Data] enter values in a matrix
[3:MatA] access Matrix A
[4:Matb] access Matrix B
[5:MatC] access matrix C
[6:MatAns] access the Answer Matrix (the last matrix calculated)
[7:det] Calculate the determinant of a matrix already defined
[8:Trn] The transpose of a matrix already defined

To add matrices MatA+MatB (MUST have identical dimensions same m and same n, m and n do not have to be the same)
To subtract MatA-MatB. (MUST have identical dimensions, see above)
To multiply MatAxMatB (See below for conditions on dimensions)
To raise a matrixe to a power 2 [x2], cube [x3]
To obtain inverse of MatA already defined MatA[x-1] [x-1] is the x to the power -1 key
Dimensions of matrices involved in operations must match.
Here is a short summary

The multiplication of structured mathematical entities (vectors, complex numbers, matrices, etc.) is different from the multiplication of unstructured (scalar) mathematical entities (regular umbers). As you well know matrix multiplication is not commutative> This has to do with the dimensions.

An mXn matrix has m rows and n columns. To perform multiplication of an kXl matrice by an mXn matrix you multiply each element in one row of the first matrix by a specific element in a column of the second matrix. This imposes a condition, namely that the number of columns of the first matrix be equal to the number of rows of the second.
Thus, to be able to multiply a kXl matrix by am mXn matrix, the number of columns of the first (l) must be equal to the number of rows of the second (m).

So MatA(kXl) * MatB(mXn) is possible only if l=m
MatA(kX3) * Mat(3Xn) is possible and meaningful, but
Mat(kX3) * Mat(nX3) may not be possible.

To get back to your calculation, make sure that the number of columns of the first matrix is equal to the number of rows of the second. If this condition is not satisfied, the calculator returns a dimension error. The order of the matrices in the multiplication is, shall we say, vital.